Creatine
| Section2 = }} Creatine is nitrogenous organic acid that occurs naturally in vertebrates and helps to supply energy to muscle and nerve cells. Creatine was identified in 1832 when Michel Eugène Chevreul discovered it as a component of skeletal muscle, which he later named creatine after the Greek word for flesh, Kreas. Function Creatine, by way of conversion to and from phosphocreatine, functions in all vertebrates and some invertebrates, in conjunction with the enzyme creatine kinase. A similar system based on arginine/phosphoarginine operates in many invertebrates via the action of Arginine Kinase. The presence of this energy buffer system keeps the ATP/ADP ratio high at subcellular places where ATP is needed, which ensures that the free energy of ATP remains high and minimizes the loss of adenosine nucleotides, which would cause cellular dysfunction. Such high-energy phosphate buffers in the form of phosphocreatine or phosphoarginine are known as phosphagens. In addition, due to the presence of subcompartmentalized Creatine Kinase Isoforms at specific sites of the cell, the phosphocreatine/creatine kinase system also acts as an intracellular energy transport system from those places where ATP is generated (mitochondria and glycolysis) to those places where energy is needed and used, e.g., at the myofibrils for muscle contraction, at the sarcoplasmic reticulum (SR) for calcium pumping, and at the sites of many more biological processes that depend on ATP.Schlattner U, Tokarska-Schlattner M, Wallimann T. (2006) Mitochondrial creatine kinase in human health and disease. Biochim Biophys Acta. 2006 Feb;1762(2):164-80. ReviewWallimann T, Wyss M, Brdiczka D, Nicolay K, Eppenberger HM. (1992) Intracellular compartmentation, structure and function of creatine kinase isoenzymes in tissues with high and fluctuating energy demands: the 'phosphocreatine circuit' for cellular energy homeostasis. Biochem J. 1992 Jan 1;281 ( Pt 1):21-40. Review.Creatine and Creatine Kinase in Health and Disease (2007) Series: Subcellular Biochemistry , Vol. 46 Salomons, Gajja S.; Wyss, Markus (Eds.) 2007, XVIII, 352 p., Hardcover ISBN 978-1-4020-6485-2Wallimann T, Tokarska-Schlattner M, Neumann D, Epand RM, Epand RF, Andres RH, Widmer HR, Hornemann T, Saks VA, Agarkova I, Schlattner U. (2007) The phospho-creatine circuit: molecular and cellular physiology of creatine kinases, sensitivity to free radicals and enhancement by creatine supplementation. In: Molecular Systems Bioenergetics: Energy for Life, Basic Principles, Organization and Dynamics of Cellular Energetics (Saks, V.A., Editor), Wiley-VCH, Weinheim, Germany, pp. 195-264 (2007)Anders RH, Ducray AD, Schlattner U, Wallimann T, Widmer HR. Functions and effects of creatine in the central nervous system Brain Research Bulletin (2008) (in press) Biosynthesis In humans, about half of the daily creatine is biosynthesized from three different amino acids - arginine, glycine, and methionine. The rest is taken in by alimentary sources. Ninety-five percent of creatine is later stored in the skeletal muscles. ; Met - Methionine; SAH - S-adenosyl homocysteine; SAM - S-adenosyl methionine.The color scheme is as follows:enzymes, coenzymes and the Met part, substrate names, the Gly part, the Arg part]] The enzyme GATM (L-arginine:glycine amidinotransferase (AGAT), EC 2.1.4.1) is a mitochondrial enzyme responsible for catalyzing the first rate-limiting step of creatine biosynthesis, and is primarily expressed in the kidneys and pancreashttp://e-collection.ethbib.ethz.ch/ecol-pool/diss/fulltext/eth15180.pdf. The second enzyme in the pathway (GAMT, guanidinoacetate N-methyltransferase, EC:2.1.1.2) is primarily expressed in the liver and pancreashttp://e-collection.ethbib.ethz.ch/ecol-pool/diss/fulltext/eth15180.pdf. Genetic deficiencies in the creatine biosynthetic pathway lead to various severe neurological defectshttp://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=602360. Controversy While creatine's effectiveness in the treatment of many muscular, neuromuscular, and neuro-degenerative diseases is documented,Creatine and Creatine Kinase in Health and Disease (2007) Series: Subcellular Biochemistry , Vol. 46 Salomons, Gajja S.; Wyss, Markus (Eds.) 2007, XVIII, 352 p., Hardcover ISBN 978-1-4020-6485-2 its utility as a performance-enhancing food supplement in sports has been questioned (see creatine supplements for more information) . Some have even proposed that its use as a performance enhancer should be banned. "...impermissible Nutritional Supplements that NCAA member institutions may not provide to student-athletes (e.g., creatine..." See section titled "Ban on creatine". Despite this, creatine remains very popular. "Creatine sales totaled $193 million in 2003 — or roughly 10% of the $1.9-billion sports supplement market, according to the San Diego-based Nutrition Business Journal Side effects Short-term use of creatine in healthy individuals is generally considered safe (see Creatine supplements#Safety). Continuous intake of excessively high dosages of creatine may lead to any of several possible side effects. While it has been hypothesized that consistently high doses could lead to hypertension due to increased water retention Is creatine bad for you?, TeenGrowth.com, studies have not yet been able to demonstrate either long-term or short term creatine supplementation result in adverse health effects.Creatine Studies, Possible Adverse Effects of Creatine Supplementation. Creatine supplementation utilizing proper cycling and dosages has not been linked with any adverse side effects beyond occasional dehydration due to increased muscular water uptake from the rest of the body. According to the opinion statement of the European Food Safety Authorities (EFSA) published in 2004 it was concluded that "The safety and bioavailability of the requested source of creatine, creatine monohydrate in foods for particular nutritional uses, is not a matter of concern provided that there is adequate control of the purity of this source of creatine (minimum 99.95%) with respect to dicyandiamide and dihydro-1,3,5-triazine derivatives, as well as heavy metal contamination. The EFSA Panel endorses the previous opinion of the SCF that high loading doses (20 gram / day) of creatine should be avoided. Provided high purity creatine monohydrate is used in foods for particular nutritional uses, the Panel considers that the consumption of doses of up to 3g/day of supplemental creatine, similar to the daily turnover rate of creatine, is unlikely to pose any risk".EFSA statement, 26 April 2006. This opinion is corroborated by the fact that creatine is a natural component in mothers' milk and that creatine is absolutely necessary for brain development in the human embryo and the baby, as well as for optimal physiological functioning of the adult human body, especially the brain, nervous system, the muscles and other organs and cells of high energy expenditure, where the creatine kinase (CK) system is highly expressed and creatine levels are high. Sources In humans, approximately half of stored creatine originates from food (mainly from fresh meat). Since vegetables do not contain creatine, vegetarians show lower levels of muscle creatine which, upon creatine supplementation, rise to a level higher than in meat-eaters. Creatine and the treatment of muscular diseases Creatine supplementation has been, and continues to be, investigated as a possible therapeutic approach for the treatment of muscular, neuromuscular, neurological and neurodegenerative diseases (arthritis, congestive heart failure, Parkinson's disease, disuse atrophy, gyrate atrophy, McArdle's disease, Huntington's disease, miscellaneous neuromuscular diseases, mitochondrial diseases, muscular dystrophy, neuroprotection, etc.). Two studies have indicated that creatine may be beneficial for neuromuscular disorders. First, a study demonstrated that creatine is twice as effective as the prescription drug riluzole in extending the lives of mice with the degenerative neural disease amyotrophic lateral sclerosis (ALS, or Lou Gehrig's disease) . The neuroprotective effects of creatine in the mouse model of ALS may be due either to an increased availability of energy to injured nerve cells or to a blocking of the chemical pathway that leads to cell death. Second, creatine has been demonstrated to cause modest increases in strength in people with a variety of neuromuscular disorders . Third, creatine has been shown to be beneficial as an adjuvant treatment for several neuro-muscular and neuro-degenerative diseases (11,12) and its potential is just beginning to be explored in several multi-center clinical studies in the USA and elsewhere. See also * Adenosine triphosphate (ATP) * Beta-alanine * Creatine kinase * Creatine methyl ester * Creatine phosphate (Phosphocreatine) * Citric acid cycle (Krebs cycle) * Creatine Ethyl Ester * Coenzyme Q10 * Idebenone * Lipoic acid * Pyritinol * Vitamin B5 * Nitric oxide References External links * NCBI Online Mendelian Inheritance In MAN (OMIM) GATM human mutation record * Quackwatch on creatine * BBC News - Creatine 'boosts brain power' * Review article on creatine's function in the neurological context (from the Science Creative Quarterly) * Creatine Supplementation for Health and Diseases on Creatine and Creatine Kinase Function * Creatine during Pregnancy and Protection of Babies against Anoxia A mouse study * Examine.com on creatine cs:Kreatin da:Kreatin de:Kreatin es:Creatina fr:Créatine id:Kreatin it:Creatina he:קראטין nl:Creatine ja:クレアチン pl:Kreatyna pt:Creatina ru:Креатин sk:Kreatín fi:Kreatiini sv:Kreatin tr:Kreatin zh:肌酸 Category:Amino acids Category:Bodybuilding supplements Category:Dietary supplements Category:Guanidines